COURTESY OF NASA/ES A/N. SMITH University of California, Berkeley and Hubble Heritage Team STScI/AURA

In Brief

When a star explodes, its bright light alerts astronomers that a supernova is in progress. A supernova also emits vast numbers of neutrinos, which are harder to detect but potentially more valuable.

The last time a supernova went off near the Milky Way, in 1987, physicists detected two dozen neutrinos. Those particles provided critical insights about supernovae and the neutrinos themselves.

The next nearby supernova, which could occur at any time, might be even more spectacular. Advanced detectors may net thousands or even millions of neutrinos, offering a new glimpse into the extreme physics of exploding stars.

In the wee hours of February 24, 1987, atop Cerro Las Campanas in Chile, Ian Shelton decided to develop the final photographic plate of the night before heading to bed. Shelton, a resident observer employed by the University of Toronto, had been tinkering with a decades-old 10-inch telescope on the mountain, training the little instrument on one of the Milky Way's galactic sidekicks, the Large Magellanic Cloud (LMC). He lifted the photographic plate out of the developing tank and examined it to make sure the three-hour-long exposure had come out well. Then something caught his attention: a curious bright spot next to a familiar spider-shaped feature known as the Tarantula nebula. He wondered what the unusual spot might be and reasoned that it was likely a flaw in the plate itself. But just to be sure, he walked out of the telescope enclosure into the dry mountain air to look up at the sky with his own eyes. He saw a bright star in the LMC that had not been visible the night before. Shelton hurried over to one of the other telescope domes on the ridge to share the news.

As he discussed his puzzling find with astronomers Barry Madore and William Kunkel in the control room, Chilean telescope operator Oscar Duhalde piped in that he had seen the same star a few hours earlier, when he stepped out for a break. Together the four of them decided the “new” star had to be a supernova, an exploding star that could briefly outshine one billion suns. No other type of astronomical object was known to change in brightness so dramatically, from being too faint to register in photographs taken the night before to being easily spotted with the naked eye. That meant Shelton and Duhalde had discovered a supernova in a satellite galaxy of the Milky Way. A few hours later, working independently, an amateur astronomer in New Zealand saw the same thing.

By midmorning, scientists around the world learned about the discovery, tipped off by phone calls from giddy colleagues and a telegram from the International Astronomical Union. Their delight had to do with the fact that “supernova 1987A” (as it came to be known) was the first one observed in our galactic neighborhood since the invention of the telescope nearly four centuries earlier.

Astronomers rushed to employ a mighty suite of optical, infrared and radio telescopes spread across the Southern Hemisphere, as well as x-ray and ultraviolet instruments onboard spacecraft, to watch the momentous event unfolding in the LMC. It was a period of frenzied activity that few scientists had ever experienced. As one ebullient astrophysicist declared, “It's like Christmas.”

These investigations of supernova 1987A provided broad support for the scenario that theorists had developed, with the help of complex simulations on supercomputers, for how an aging massive star self-destructs, with its core collapsing into a tightly packed ball of neutrons—called a neutron star—or into a black hole and with its expelled outer layers spreading outward to form a glowing cloud of debris. Yet the celebration was not limited to astronomers. For particle physicists, other observations of the supernova provided important clues to the nature of the ghostly subatomic particles known as neutrinos. Together the diverse studies of the 1987 supernova have built up anticipation of a similar stellar collapse right in our own galaxy—an event that could occur at any time and that should answer lingering questions about star death and the nature of neutrinos. This time neutrino hunters will probably be the first to detect the event.